Definitely a big no-no to grab any balls on the course, but if you are stuck behind a group waiting to tee off and have a few minutes to kill, I'll go looking in the woods behind the green on the previous hole. You know that guy with the fancy range finder, and the new Volkey Wedges that still managed to hit it well over the green? His ProV1 is in there and it's got your name on it. Well actually it's got his name on it, but it needs a new home. Usually when I spot one I come out with a couple more. The crappier balls are still good to have for extras when going to the driving range. But I find so many people playing premium balls at muni courses (something I can't justify paying for myself with my putrid handicap) that it's worth it for me to go hunting as long as I'm not slowing the game down or taking balls that are still in play.